Some species of nocturnal moths decrease the chances of their capture by detecting the sonar pulses of insectivorous bats and taking several forms of evasive action. Acoustic input to noctuid moths' central nervous systems consists of only two acoustic fibers from each ear; output consists of differential changes in wing angle-of-attack. It is proposed that this situation offers a tempting opportunity to work out the neuronal organization of a simple behavior pattern of obvious survival value. Evidence has been collected that this avoidance behavior is evitable, i.e., not invariant, especially under experimental conditions. Neurophysiological studies are in progress seeking to identify and delineate neuronal mechanisms in the moth brain that a) promote and sustain reflex changes in wing movement under some conditions and b) suppress them under others. Attempts are being made also to define conditions responsible for this evitability. It is planned to make similar studies of mechanisms controlling avoidance behavior in the cockroach.